Light-modulating device



Nov. 22, 192 7.

1,650,166 H. VOGT ET AL LIGHT MODULATING DEVICE Filed Aug. 18, 1925 ll,

Z4 fig mit Z9' 4 6a la 5 i fla 1 l n'n'A'A'A'nA'A'IvAV /s /4 fz w e s 465,; Foret-#fu Patented Nov.l'22, 1927.

UNITED STATES PATENT ori-Ica HANS VOGT, OF BERLIN-WILHERBDOBF, AND JOSEF ENGL 4ANZI) JOSEPHMASSOLLE, 0I'

BEBLINfGBUNEWALD, GERMANY, ABSIGNORS TO TBI-ERGON, A.G., 0F ZURICH, SWITZERLAND, .A CORPORATION OF SWITZERLAND.'

LIGHT-MODULATING :envien Application led August 18, 1925, Serial No. 51,074, and in Germany February 21, 1922.

The application relates to li ht modulating devices 'and more particular y to devices in which the intensity of illumination of a source of light is acoustically-modulated, in a system in which the acoustically-modulated light 4is caused to photographically form a sound record on a moving lm strip or the like. Further, as to some features of the invention, the same relates particularly to improvements in light modulating devices in which lthe source of light is an evacuated tube containing a certain proportionv of a desired gas in which a luminous discharge within the tube is caused, which discharge may be acoustically-modulated by su plying the tube with acoustically-mod ated current, such tubes or devices being known as glow tubes or luminous gas discharge The invention relates in part toarrangements whereby a e luminous gas vdischarge tube may be connected to and supplied from i a thermionic amplifier in such a manner that certain diilcultles commonly experienced when vacuum tube amplifiers are connected in series with luminous gas dischar e tubes.

will be overcome. As to this it may e noted that gas discharge tubes have, entirely or in part, a negative voltage curve. It, ltherefore, followsthat if such a tube is connected in series with the usual form of vacuum tube amplifier, disproportionalities are caused between the variations in intensities ofthe luminous discharge and the variations of the electrical current or voltage by whichthegas discharge device is operated. A An object of the present invention is'the provision of means for overcoming or decreasin this diiliculty.

e invention also relates to im rove-l ments in connection with the operation of the acoustically-modulated light by means of amplifying devices in which improved connections are provided between the various parts and in which a loud speaker or other sound reproducing device is additionally provided in the system, by' which a per son supervising the sound recordin system, or su rvising the operation of te light modu ating apparatus, generally, may determine whether the o eration is being eiec'- tively erformed. hus in sound `recording it has een found desirable to keep the detive voltage characteristic of the gas 1scharge tube may be utilized for coupling the sound reproducing device referred to, to the amplifier-gas discharge tube circuit.

. The invention comprises various` combinations of parts and details of constructionv which will be more fully described in the following specification and which will b'e particularly pointed out in the appended claims.

In yorder that the invention may be more fully understood attention is-hereby directed to the accom anying drawings forming part of this application and illustrating certain features and embodiments of the invention.

In the drawin Figure 1 is .a diagram illustrating the re ation between volta e and current of a luminous gas dischargetu e;

Fig. 2 is a diagram illustrating the relations between output current and input po-l tential of the usual form of thermionic amplifier connected in series with a luminous gas discharge .tube having a negative voltage characteristic;

Fig. 3 is a diagrammatic view illustrating connections between an amplifier and a luminous gas discharge tube in a sound recording1 system comprised within the invention an Fig. 4 is a diagrammatic view showing a modified form of the invention.

In Figure 1 the characteristic curve, a, of a luminous gas discharge device will be seen to lbe a negative voltage curve, the volta 'V supplying the tube being indicated by t e vertical axis and the current I supplied to the Aglow discharge tube. by the horizontal a cathodefjand one grid and one anode, theexamplen a gas dislooY ` 35 anode penetration, preferably current curve of which depends essentially Aon the penetratingx anode potential (i. e., the otential acting t rough the grid), the vfolowing conditions may develop. When the Iv current output ofthe amplifier increases, the volta e at the gas discharge tube decreases,

. and t e current may continue to increase because of av simultaneously increasing anode voltage of the amplifier. In the case of a diminishing plate current, the opposite 'effect takes place, since in this case the voltage of the gas discharge tube will be rising. Consequently the current curves of the ampliiier connected in series with the glow discharge tube do not correspond, but form a loop which causes considerable disproportionalities in the conversion of electrical waves into variations of -light,;such for example as in a the photographic recording 'of sound as mentioned above.

This state of aiairs is indicated in the diagram of Fig. 2 in which the curve b may be taken as representing the relations between the late current, and grid potential of the ampliiier tube connected in series with a glow discharge tube, in the case of an 1n` creasing plate current, while the other curve b forming a loop with curve b', represents the relation between the plate current an grid potential in such a system when the platecurrentis diminishing,

' This diculty may be lovercome to greater f or' lesser extent in several ways. Thus,

amplifier tubes may be used of less than Ampliers having a single plate, grid,

v a suflicientl low` anode penetration can, owever, har ly be used as a practical matter because the plate and lament andhavin 0 potential which is necessary for obtainingan adeluate current output in .case of negative gri potentials becomes too high. This diiliculty may be overcome toa considerable ex- 'tent by theuse of an anode-screening electrode interplosed between the plate and grid `of the amp 'fier,.with thescreenin member provided with a eater potentia, relative to the. filament, t an that of the working anode or plate as disclosed in our'applica- 5 tion Seria No. 458,635, filed April 4, 1921,

improvements in electron tubes. .With such an arrangement the electro-static lines of force from the --working anodeor plate through the openings of the grid is greatly decreased hi trode, or auxiliary anode, provides a-suificiently large current .out ut for the tube.

The harmful' eiect of t e negative voltage "characteristic of the glow discharge tube 5 may also be diminishedby'connectingolimc resistances in the out 'ut circuit otheampli'- y iier,-such.resistances Yein used eitlier'alone: *10mnaddition to the use 'o other means such asthe anode-screening electrode @referred to;

Such a resistance reduces the divergsincev having 'a 'f low e the anode screening elec- Leconte between the current curves'indicated in Fig. 2, since it takes up a part of the injurious potential. Similar results may be obtained if the gas discharge tube is connected in parallel with the am 'lifier tube, by which the glow discharge tu e is fed in the manner lndicated in our ap licat-ion Serial No. 545,375, ampliiier coupling, lfiled March 20,

now Patent No. 1,555,301, datedSeptember 29, 1925. In that case the ohmic resistance, which is desired, is afforded by the coupling resistance or resistances through which the B battel current is supplied to the output circuito the amplifier and to the terminals of the 4glowA discharge device. 80 Suitable connections are described and-illustrated in our said Patent No. 1,555,301.

In Fi 3 we haveY illustrated a system in which t e diiculties referred -toare overcome by the conjoint use of anolimic resistance in the connection between the amplifier and the glow discharge tube, and a protecting or anode-screening electrode in the amplifier. This figure also shews the use of the resistance referred to for coupling an electro-static superviso telephone or sound reproducing device to t e system.

In Fig. 3 the amplifier 1,may be prod vided with the usual Iilament 2grid- 3 and plate 4 and in addition 'with the anode- 95 screening electrode 5 inter sed between the plate 4 and 0rid 3, electro e 5 preferably bein of a mesllied or gri -like construction.

he luminous gas d scharge device 6 comprises an evacuated t be containing a desired 'proportion of a suitable gas such as,l

for example, argon, this tube. having an anode 7 and a cathodev 8. vDischarge between .tliese electrodesl reduces a luminous glow or cloud, chiefly a jacent to the, end of the cathode. The intensity of illumination of this cathodic glow is utilized for making a photographic record of varyin density u on a moving sensitized 'ilm strip or the li e. Glow dischar e tube 6 is indicated as being contained wit in a tube 9. The light emitted from' the glow discharge tube may be concentrated by a suitable optical system upon a narrow slit (not illustrated), the ima e of which -is 'proJected upon a moving sensitized iilm strip f. v

The output circuit of amplifier 1 may be traced as extending from plate 4 of the amplier through 'a variable resistance 10 e an Va resistance-11 and thence by a conductor 12 to the cathode 8 of the glow discliar e tube, the circuit continuing from the ano e 7 of the glow discharge tube throu h battery 13,'by conductor 14 `back tote iila= 125 ment 2 ofthe amplifier which may be consideredas grounded. f The glow discharge tub willbe isu vplied with amplified acoustically-modulat our?4 rent when,y acoustically-modulated potentie of the amdplifier 1, and the light emitted by the glow ischarge tube 6 will be correspondingly acoustically-modulated.

The auxiliary electrode of the amplifier isconnected by conductor to a point of positive potential in the source 13. The screening electrode 5 of the amplifier will, therefore, be of a higher potential than the plate 4, since the latter is connected to the positive terminal of the source'l3 through a considerable resistance which may comprise the internal resistance of the glow discharge tube 6 or the resistances 10 and 1l, or both. The ditiiculties due to the negative voltage characteristic of the glow discharge tube are, therefore, overcome in the embodiment of the invention-here illustrated by the use of the screening electrode 5 together with the use of the resistance l1 and as much of the variable resistance 10 as maybe included in the plate circuit of the amplifier.

A resistance 16 of large value is shown as connected in parallel with the output of amplifier 1. Accordingly, a small current will continue to fiow through the gas discharge tube 6, from battery 13, even when for any reason the impedance of theamplif ing tube 1 becomes infinitely high. This reslstance 16 is used to prevent complete interruption of the current feeding glow discharge tube 6 in any case, because interruption of this current would entail difficulties in the immediate restarting of the glow discharge current through tube 6. f

The sound reproducing device reviously referred to preferably takes the orm of a condenser telephone type of loud speaker indicated at 17 which may be mounted within a sound proof enclosure indicated at 18. The

lcondenser telephone comprises a fixed plate element 19 and a movable plate element in -the form. of a diaphragm 20. This tele' phone is connected in parallel with resistances 10 and 11 by means of conductors 21 and 22, a condenser 23 bein positioned in one of these connections. T e variable re-` sstance 10 enables the volume of the sound produced by the condenser telephone 17 to be adjusted as desired, a/connection 24 extending from conductor 21 to an adjustable contact on the resistance 10. A resistance 25 lis employed'to drain 0E 'any electric charge upon film f, are-being properly carried out. T 1e operator in-the listening-in chamber 18 may adjust the degree of amplification of the system from time to time as desired by suitable means. i

Fig. 4 is a somewhat simplified diagram illustrating an embodiment of the invention -in which the amplifier 1 is not provided with the anode-screening electrode 5, which has been described in connection with Fig. 3. The luminous gas discharge tube 6a is connected in series with the output terminals of the amplifier l, ythe source ot' potential 13 and the resistance l1 being included in the circuit'. Thetelephone or'loud speaker 17a is connected in parallel with resistance ll, this sound reproducing device preferably being a loud speaker of the condenser telephone type, as described above. With this form of apparatus the resistance 11a alone is depended on for overcoming the harmful effects of the negative voltage curve of the gas discharge device and this resistance is additionally used as a means for coupling the tele hone 17.

We c aim: i

1. In light-modulating devices, the combination .of a luminous gas discharge tube having a negative voltage curve, a thermionic amplifier having input and output terminals, a source of potential, a resistance, and means for connecting the amplifier outputA terminals, 'discharge tube, source and resistance in series, said resistance being adapted to largely overcomel the effect of the negative voltage characteristic of said discharge tube in causing disproportionality between the variations of intensity of luminous discharge of said tube and the variations of potential at the input terminals of said amplifier.l 4

2. In light-modulating devices, the combination of a luminous gas discharge tube, a

. thermionic amplifier having anode, cathode,

grid and an anode-screening electrode, a source of potential, a resistance, and means for connecting the amplifier anode and cathode, discharge tube, source and resistance in series and for connecting said screening electrode to. a point in said connections of higher potential than that of said anode.

3. In light-modulating devices, the combination of a luminous gas discharge tube, a thermionic amplifier having anode, cathode, grid and an anode-screening electrode, a source of potential, means for connecting the positive terminal of said source through said dischar e tube to said anode and for connecting t e negative terminal of said source to said cathode, and a connection between said screening electrode and a point in said source of higher potential than that of said amplifier anode.

4. In light-modulating devices, the combination of a luminous gas discharge device `mionic ampli nefative voltage curve, a theriier tube, having input and output terminals therein, a source of potential, said source being connected to the output terminals of Asaid amplifier tube andv the latter being connected to supply current to said gas discharge device, and means adapted largely to overcome the effect of the negative voltage characteristic of said, discharge device in causing disproportionality between thel variations of intensity of lumihaving a nous discharge of said device-andthe variations of potential'at the input terminals of said amplifier. 5. In light-modulating devices, the combination of a thermionic amplifier, having .an input circuit and an output circuit, a luminous gas discharge device anda resistance, both in said output circuit, and a sound reproducing device in shunt with said resistance. 6. In light-modulating devices, the combination of a 'thermionic amplifier having input and output terminals, a high resistance connected across said output terminals, a secondv resistance and a luminous gas discharge device connected in series with said output terminals, anda source of potential connected to said output terminals.

7. In light-modulating devices, the combination of a thermionic. amplifier. having an output circuit, a luminous gas discharge device and a-resista'nce, both in said outputv circuit, and a.4 condenser telephone connected across said resistance. 8. In light-modulating devices, the combination of a thermionic amplifier having output terminals, a variable resistance, .a luminous gas discharge device and a source of 4c sound reproducer, and means for connecting potential in series with "said terminals, a

the latter across a greater or less amountof said resistance. y

HANS VOGT. JOSEF ENGL. JOSEPH MASSOLLE. 

